Apparatuses and method for over-voltage event protection

ABSTRACT

Circuits, integrated circuits, apparatuses, and methods, such as those for protecting circuits against electrostatic discharge events are disclosed. An example apparatus comprises a thyristor coupled to a node and configured to limit the voltage and discharge the current associated with an over-voltage event at the node. The over-voltage event includes a negative voltage having a magnitude that exceeds a trigger voltage of the thyristor, The example apparatus further comprising a transistor coupled to the thyristor and configured to adjust the magnitude of the trigger voltage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/795,425, filed Mar. 12, 2013. This application is incorporated byreference herein in its entirety and for all purposes.

TECHNICAL FIELD

Embodiments of the disclosure relate generally to integrated circuits,and more particularly, in one or more of the illustrated embodiments, tocircuitry including a trigger circuit with an electrostatic dischargeprotection circuit.

BACKGROUND OF THE DISCLOSURE

Integrated circuits are connectable to external circuitry through inputnodes, output nodes, or input/output nodes such as bond pads, inputpads, input/output pins, die terminals, die pads, contact pads, and soforth. The integrated circuitry often includes operational circuitrythat includes circuit components, such as transistors, that aresusceptible to damage caused by over-limit electrical events, forexample, voltages caused by electrostatic discharge (ESD) duringhandling, testing and operation of the integrated circuit. An over-limitelectrical event (e.g., an ESD event) that may cause damage to thecircuitry of the integrated circuit unless adequately protected.Typically, the susceptible circuit components may be protected fromover-limit electrical events via an ESD protection circuit to preventdamage caused by an over-limit electrical event. Typically, an ESDprotection circuit is associated with one of the above-mentioned nodes.

ESD protection circuits may include circuitry that provides a conductivepath to a reference voltage such as ground and/or to a voltage supplysuch as VCC, to limit or clamp the voltage (e.g., by discharging orshunting the current) associated with the over-limit electrical eventbefore operational circuitry of the integrated circuit is damaged.Although some circuit components may be capable of limiting sometransient ESD voltage without some circuit components may be capable oflimiting some transient ESD voltage without damaging circuit components,other circuit components may be damaged as a result of any ESD voltage.For example, high-speed input or output circuits (or other specializedcircuit components) may tolerate little to no transient ESD voltage orcurrent. In other words, some circuits may not be self-protecting. Also,as semiconductor devices continue to shrink, the circuit componentsbecome more prone to and less tolerant of over-limit electrical events.And, even if the circuit components can tolerate a small level oftransient ESD voltage or current, the ESD protection circuit's breakdownvoltage may be lower than the breakdown voltage of for example, thecircuit components. In this case, dedicated ESD circuits may be added tohelp clamp the ESD voltage level below the breakdown voltage of thetransistors.

Some dedicated ESD circuits include circuit components that exhibit a“snap-back” characteristic. Generally, a snap-back characteristicprovides a trigger condition which, when exceeded, causes the circuit toenter a low-impedance state. The low-impedance state is maintained whilethe electrical condition on the node exceeds a minimum hold. condition(e.g., minimum holding voltage and/or current levels). Examples ofconventional circuits having snapback characteristics include overdrivenmetal-oxide-semiconductor (MOS) transistors.

In designing an adequate protection circuit using a snapback circuit,the trigger condition must be sufficiently low to provide protectionbefore a breakdown condition occurs for operational circuitry. Examplesof conventional protection circuit for operational circuitry coupled toa negative potential node may include an ESD clamp formed using largep-type field-effect transistors (PFETs). In this case, for example,should a large negative voltage (with respect to a reference voltage,such as ground) from an over-limit electrical event be provided to thenode, the transient ESD voltages may be limited and the ESD current maybe discharged through the large ESD clamp to ground. However, the largeESD clamp requires a large footprint to implement. An ESD voltageprotection circuit is capable of protecting the operation circuitry, yetrequiring a smaller footprint is desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary apparatus including anelectrostatic discharge (ESD) protection circuit according to anembodiment of the present disclosure;

FIG. 2 is a block diagram of an exemplary apparatus including an ESDprotection circuit according to an embodiment of the present disclosure;

FIG. 3 is a block diagram of an exemplary apparatus including an ESI)protection circuit according to an embodiment of the present disclosure;

FIG. 4 is a cross-sectional diagram of an integrated circuitimplementing the ESD protection circuit of FIG. 3 according to anembodiment of the disclosure; and

FIG. 5 is a schematic diagram of a memory including an ESD protectioncircuit according to an embodiment of the disclosure.

DETAILED DESCRIPTION

Certain details are set forth below to provide a sufficientunderstanding of embodiments of the disclosure. However, it will beclear to one skilled in the art that embodiments of the disclosure maybe practiced without these particular details. Moreover, the particularembodiments of the present disclosure described herein are provided byway of example and should not be used to limit the scope of thedisclosure to these particular embodiments. In other instances,well-known circuits, control signals, timing protocols, and softwareoperations have not been shown in detail in order to avoid unnecessarilyobscuring the disclosure.

FIG. 1 illustrates an apparatus including an electrostatic discharge(ESD) protection circuit according to an embodiment of the disclosure.As used herein, examples of apparatuses may include an integratedcircuit, a memory device, a memory system, an electronic device orsystem, a smart phone, a tablet, a computer, a server, etc. Theapparatus 100 may include a protected circuit 105, and a protectioncircuit 115. The protection circuit 115 may be coupled to a pad 110 inparallel with the protected circuit 105.

The protection circuit 115 may be configured to help protect theprotected circuit 105 from harmful events. For example, the protectioncircuit 115 may help protect electrical components of the protectedcircuit 105 from being damaged by over-limit electrical events (such asan over-voltage event), for example, electrostatic discharge (ESD), orelectrical noise events. Although over-limit electrical events or othernoise may come from any source within the integrated circuit, it mayalso come from an external source via the pad 110 or other externalnode. For example if a user, or a metallic part or any other objecttouches the pad 110, that contact may induce an over-limit electricalevent. The protection circuit 115 may help limit (e.g., clamp) thevoltage and discharge the current associated with the over-limitelectrical or other event to a reference node 150. In some embodiments,the protection circuit may limit the voltage associated with theover-limit electrical or other event by discharging a current associatedwith the over-limit electrical or other event to a reference node 150.The protection circuit 115 may further help limit (e.g., clamp) thevoltage.

The protection circuit 115 may include a conductive path circuit 120 anda trigger circuit 130. The conductive path circuit 120 may provide acurrent discharge path between the pad 110 and the reference node 150.The conductive path circuit 120 may at least partially discharge anelectrical condition by discharging current between the pad 110 and thereference node 150 responsive to a voltage difference between the pad110 and the reference node 150 exceeding a magnitude of a triggervoltage of the conductive path circuit 120. The trigger circuit 130 maybe configured to adjust the trigger voltage of the conductive pathcircuit 120 based on a value of the control node 140. For example,responsive to the control node 140 having a first value, the triggercircuit 130 may cause the conductive path circuit 120 to have a firsttrigger voltage. Further, responsive to the control node 140 having asecond value, the trigger circuit 130 may cause the conductive pathcircuit 120 to have a second trigger voltage. In some embodiments, avoltage of the control node 140 may be modulated such that the voltageof the control node 140 has the first value while the apparatus 100 isin an operational mode, and may have the second. value while theapparatus 100 is in an ESD mode. In some embodiments, the first value ofthe control node 140 may be set to a VCC voltage and the second value ofthe control node 140 may be a reference voltage, such as ground.

In some embodiments, the pad 110 may be a negative voltage node whilethe apparatus is in an operational mode, and the conductive path circuit120 may be configured to provide a negative discharge path between thereference node 150 and the pad 110. The conductive path circuit 120 mayinclude a thyristor (e.g., a silicon-controlled rectifier (SCR))configured to, responsive to a magnitude of a voltage difference betweenthe pad 110 and the reference node 150 exceeding (e.g., is more negativethan) the trigger voltage, provide a conductive path between the pad 110and the reference node 150. The conductive path may be used to dischargean electrical current provided to the pad 110. The conductive pathcircuit 120 may continue to discharge the current through the conductivepath circuit while in a holding condition (e.g., until a magnitude of avoltage differential between the pad 110 and the reference node 150 isreduced to less than a holding voltage of the conductive path circuit120).

In some embodiments, the trigger circuit 130 may include a p-type FET(PFET) configured to adjust the trigger voltage of the conductive pathcircuit 120 based on a state of the PFET. For example, while the PFET isin a first state, the conductive path circuit 120 has a first triggervoltage and while the PITT is in a second state, the conductive pathcircuit 120 has a second trigger voltage. The state of the PFET may becontrolled responsive to a value (e.g., voltage) of the control node140. The PFET may be coupled in parallel with the conductive pathcircuit 120, with a gate of the PFET coupled to the control node 140.Although FIG. 1 illustrates the protected circuit 105 in parallel withthe protection circuit 115, a protection circuit may also be placed inseries with the protected circuit or even merged with the protectedcircuit. In some embodiments, the conductive path circuit 120 mayinclude additional circuitry configured to discharge electrical currentsprovided to the pad 110 responsive to a positive ESD or other noiseevent.

FIG. 2 illustrates an apparatus 200 according to an embodiment of thedisclosure. The apparatus 200 includes a protected circuit 105 and aprotection circuit 215. The protected circuit 105 is similar to thatshown in FIG. 1. The protection circuit 215 may be coupled to a pad 210in parallel with the protected circuit 105. The protection circuit 215may include a conductive path circuit 220 coupled in parallel with atrigger circuit 230. The trigger circuit 230 may include a triggerbipolar junction transistor (BJT) 232 and a trigger transistor 234.

In some embodiments, the trigger circuit 230 includes the trigger BJT232 merged with the trigger transistor 234. The trigger BJT 232 is“merged” with the trigger transistor 234 in that the body of the triggertransistor 234 shares an n-well with at least a portion of the triggerBJT 232, as will be described further in FIG. 4. Returning to FIG. 2,however, the trigger circuit 230 may be visualized as including thetrigger BJT 232 and the trigger transistor 234. The trigger BJT 232 maybe a lateral p-n-p type BJT, with an emitter and a base coupled to thereference node 150, and a collector coupled to the conductive pathcircuit 220. In some embodiments, the trigger transistor 234 may be aPFET with a source coupled to the reference node 150, a drain coupled tothe conductive path circuit 220, and a gate coupled to the control node240.

In operation, the protection circuit 215 may help protect the protectedcircuit 105 by limiting the voltage and discharging at least somecurrent resulting from an over-limit electrical event (or other noiseevent) rather than having the protected circuit 105 manage that currentand voltage. For example, the protection circuit 215 may be configuredto limit the voltage (e.g., by discharging a current) from the referencenode 150 to the pad 210 via the conductive path circuit 220, responsiveto a negative (e.g., relative to a voltage of the reference node 150)voltage provided to the pad 210 exceeding a trigger voltage. The triggervoltage may be adjusted based on a state of the trigger transistor 234.The state of the trigger transistor 234 may be controlled based on avalue of the control node 240. For example, the trigger voltage set bythe trigger transistor 234 may be greater when a voltage of the controlnode 240 exceeds a threshold voltage of the trigger transistor 234(e.g., the trigger transistor 234 is in a first state) than when thevoltage of the control node 240 is less than a threshold voltage of thetrigger transistor 234 (e.g., the trigger transistor 234 is in a secondstate). In some embodiments, the trigger transistor 234 may be in thefirst state (e.g., the voltage of the control node 240 is greater thanthe threshold voltage of the trigger transistor 234) while the apparatus200 is in an operational mode and the trigger transistor 234 may be inthe second state (e.g., the voltage of the control node 240 is less thanthe threshold voltage of the trigger transistor 234) while the apparatus200 is in an ESD mode. The protection circuit 215 including the triggercircuit 230 having the trigger transistor 234 to adjust the triggervoltage of the conductive path circuit 220 may have a smaller footprintas compared with conventional ESD protection circuits that include largePFETs.

FIG. 3 illustrates an apparatus 300 according to an embodiment of thedisclosure. The apparatus 300 includes a protected circuit 105 and aprotection circuit 315. The protected circuit 105 is similar to thatshown in FIGS. 1 and 2. The protection circuit 315 may be coupled to apad 310 in parallel with the protected circuit 105. The protectioncircuit 315 may include a conductive path circuit 320 coupled inparallel with a trigger circuit 330. The trigger circuit 330 may includea trigger transistor 334 and a trigger BJT 332. In some embodiments, thetrigger circuit 330 includes the trigger BJT 332 merged with the triggertransistor 334. In some embodiments, the trigger BJT 332 may be alateral p-n-p type BJT, with an emitter and a base coupled to thereference node 150, and a collector coupled to the conductive pathcircuit 320, In some embodiments, the trigger transistor 334 may be aPFET with a source coupled to the reference node 150, a drain coupled tothe conductive path circuit 320, and a gate coupled to the control node340. The protection circuit 315 may correspond to the protection circuit115 of FIG. 1 and the protection circuit 215 of FIG. 2. The conductivepath circuit 320 may be a negative direction (e.g., from the referencenode 150 to the pad 310) SCR having a trigger voltage controlled by thetrigger circuit 330.

The conductive path circuit 320 includes a negative direction SCRcoupled between the pad 310 and a reference node 150. The SCR isrepresented in FIG. 3 as a first BJT 322 and a second BJT 324. The firstBJT 322 may be an n-p-n type BJT and the second BJT 324 may be p-n-ptype BJT, and as will be described in more detail below, may share ap-type base-collector region and sharing an n-type collector-baseregion. The conductive path circuit 320 may be configured to limitvoltage between the reference node 150 and the pad 310 (e.g., bydischarging a current) responsive to a magnitude of voltage differentialbetween the pad 310 and the reference node 150 exceeding (e.g., beingmore negative than) a trigger voltage. The trigger circuit 330 may beconfigured to adjust the trigger voltage of the conductive path circuit320. For example, the trigger voltage of the conductive path circuit 320based on state of a trigger transistor 334 of the trigger circuit 330.

Although FIG. 3 illustrates the first BJT 322 and the second BJT 324 asseparate devices, as illustrated in FIG. 4 and discussed below, thefirst BJT 322 and the second BJT 324 may not be separate devices butrather may share doped regions and, thus, form an n-p-n-p typethyristor, rather than form two distinct ans. For example, the base ofthe first BJT 322 may share the same doped region (e.g., an isolatedp-well ISO-PWELL 460 of FIG. 4) as a collector of the second BJT 324,and a collector of the first BJT 322 may share the same doped region(e.g., an n-well NWELL 410 of FIG. 4) as a base of the second BJT 324.Returning to FIG. 3, however, the SCR of the conductive path circuit 320may be visualized as including the first BJT 322 and the second BJT 324.

Further, although FIG. 3 illustrates the trigger BJT 332 and the triggertransistor 334 as separate devices, as illustrated in FIG. 4 anddiscussed below, the trigger BJT 332 and the trigger transistor 334 maynot be separate but rather may share doped regions. For example, acollector of the trigger BJT 332 may share the same doped region (e.g.,a pH-region 470 of FIG. 4) as a drain of the trigger transistor 334, andan emitter of the trigger BJT 332 may share the same doped region (e.g.,a p+ region 472 of FIG. 4) as a source of the trigger transistor 334.Additionally, a base of the trigger BJT 332 may share the same dopedregion (e.g., the NWELL 410 of FIG. 4) as a body of the triggertransistor 334.

In operation, the conductive path circuit 320 provides a conductive pathbetween the reference node 150 and the pad 310 responsive to a voltagedifferential between the pad 310 and the reference node 150 exceeding(e.g., being more negative than) a trigger voltage. As known, SCRsexhibit a “snapback” current-voltage relationship when triggered. Thesnapback characteristics of the SCR of the conductive path circuit 320are advantageously used to protect the protected circuit 105. Thetrigger transistor 334 of the trigger circuit 330 may be configured toeffectively adjust the trigger voltage for the conductive path circuit320 through gate modulation. For example, the control node 340 may havea first voltage. Responsive to the control node 340 having the firstvoltage, the trigger transistor 334 may be in a first state. Responsiveto the trigger transistor 334 being in the first state, the conductivepath circuit 320 may have a first trigger voltage. Further, the controlnode 340 may have a second voltage. Responsive to the control node 340having the second voltage, the trigger transistor 334 may be in a secondstate. Responsive to the trigger transistor 334 being in the secondstate, the conductive path circuit 320 may have a second triggervoltage. As a result of the conductive path circuit 320 having eitherthe first trigger voltage or the second trigger voltage, the conductivepath circuit 320 may trigger at a sufficiently low voltage to dischargecurrent resulting from an over-limit electrical event and to furtherclamp a voltage protected circuit 105 to a low enough voltage to preventthe protected circuit 105 from being damaged by the over-limitelectrical event.

FIG. 4 illustrates a apparatus 301 depicting a cross-section view of theprotection circuit 315 of FIG. 3 according to an embodiment of thedisclosure implemented an isolated p-well ISO-PWELL 460 within an n-wellNWELL 410, The NWELL 410 is doped with an n-type dopant and the ISO-PWELL 460 is doped with a p-type dopant.

As explained above, although FIG. 3 illustrates the first BJT 322 andthe second BJT 324 of the conductive path circuit 330 as separatedevices, as illustrated in FIG. 4, the first BJT 322 and the second BJT324 may not be separate but rather may share doped regions. Referring toFIG. 4, the first BJT 322 (of FIG. 3) of the conductive path circuit 320includes an n+ region 464 (e.g., the emitter) coupled to the pad 310,the ISO-PWELL 460 (e.g., the base), and the NWELL 410 (e.g., thecollector) coupled to the reference node 150 via the n+ region 480.Further, the second BJT 324 (of FIG. 3) of the conductive path circuit320 includes the ISO-PWELL 460 (e.g., the collector), the WELL 410(e.g., the base), which is shared with the base of the trigger BJT 332,and a p+ region 470 (e.g., the emitter) coupled to the reference node150, which is shared with the collector of the trigger BJT 332. Thus,the conductive path circuit 320 may be a single p-n-p-n device (e.g., ap (p+ region 470)−n (NWELL 410)−p (ISO-PWELL 460)−n (464) device).

Further, as explained above, although FIG. 3 illustrates the trigger BJT332 and the trigger transistor 334 as separate devices, as illustratedin FIG. 4, the trigger BJT 332 and the trigger transistor 334 of thetrigger circuit 330 may share doped regions. Referring to FIG. 4, thetrigger BJT 332 (of FIG. 3) of the trigger circuit 330 includes the p+region 470 (e.g., the emitter) coupled to the reference node 150, theNWELL 410 (e.g., the base) coupled to the reference node 150 via the n+region 480, and the p+ region 472 (e.g., the collector). Further, thetrigger transistor 334 of the trigger circuit 330 includes the p+region470 (e.g., the source), which is shared with the emitter of the triggerBJT 332, a gate 474 (e.g., the gate) coupled to the control node 340, ap+ region 472 (e.g., the drain), which is shared with the collector ofthe trigger BJT 332, and the NWELL 410 (e.g., the body), which is sharedwith the base of the trigger BJT 332. Thus, the trigger circuit 330 maybe a single p-n-p device with a gate (e.g., a p (p+ region 470)−n (NWELL410)−p (p+ region 472) device with a gate 474. The p+ region 472 may becoupled to the ISO-PWELL 460 via the p+ region 462.

In operation, the trigger circuit 330 of the apparatus 301 may beconfigured to adjust a trigger voltage of the apparatus 301 based on avoltage of the control node 340. Responsive to a negative voltagedifferential between the pad 310 and the reference node 150 exceeding(e.g., being more negative than) the trigger voltage (e.g., responsiveto an over-limit electrical event or other noise event), the conductivepath circuit 320 may provide a conductive path between the referencenode 150 and the pad 310. The trigger circuit 330 is configured toadjust a voltage of the ISO-PWELL 460 based on a state of the triggercircuit 330, which adjusts the trigger voltage of the trigger circuit330. The state of the trigger circuit 330 is controlled responsive to avoltage of the control node 340. For example, responsive to the controlnode 340 having a first voltage, the trigger circuit 330 is in a firststate. Based on the trigger circuit 330 being in the first state, theconductive path circuit 320 has a first trigger voltage. Further,responsive to the control node 340 having a second voltage, the triggercircuit 330 is in a second state. Based on the trigger circuit 330 beingin the second state, the conductive path circuit 320 has a secondtrigger voltage, In embodiment, the first mode is an operational modeand the second mode is ESD protection mode. In some examples, the firstvoltage of the control node 340 is greater than the second voltage ofthe control node 340, and the first trigger voltage of the conductivepath circuit 320 is greater than the second trigger voltage of theconductive path circuit 320. For example, during an operational mode, anegative operational voltage (e.g., 0 to −4.1 volts) is expected at thepad 310. Thus, the trigger voltage should be lowered to a voltage thatis more negative than the expected negative operational voltage at thepad 310 to avoid interfering with operation of the protected circuit105, yet providing protection to the protected circuit 105 from damagingvoltages at the pad 310. Further, while in an ESD mode, little or novoltage is expected at the pad 310. Thus, the trigger voltage may be setto a value that is less negative than the trigger voltage used duringthe operational mode to prevent the pad 310 from building a charge.

FIG. 5 illustrates a portion of a memory 500 according to an embodimentof the present disclosure. The memory 500 includes an array 502 ofmemory cells, which may be, for example, DRAM memory cells, SRAM memorycells, flash memory cells, phase change memory cells, or some othertypes of memory cells. The memory 500 includes a command decoder 506that receives memory commands through a command bus 508 and generatescorresponding control signals within the memory 500 to carry out variousmemory operations. Row and column address signals are applied to thememory 500 through an address bus 520 and provided to an address latch510. The address latch then outputs a separate column address and aseparate row address.

The row and column addresses are provided by the address latch 510 to arow decoder 522 and a column address decoder 528, respectively. Thecolumn address decoder 528 selects bit lines extending through the array502 corresponding to respective column addresses. The row decoder 522 isconnected to word line driver 524 that activates respective rows ofmemory cells in the array 502 corresponding to received row addresses.The selected data line (e.g., a hit line or bit lines) corresponding toa received column address are coupled to a read/write circuit 530 toprovide read data to a data output circuit 534 via an input-output databus 540. An output pad 542 coupled to the data output circuit 534 isused for electrically coupling to the memory 500. Write data are appliedto the memory array 502 through a data input circuit 544 and the memoryarray read/write circuitry 530. An input pad 546 coupled to the datainput circuit 542 is used for electrically coupling to the memory 500.The command decoder 506 responds to memory commands applied to thecommand bus 508 to perform various operations on the memory array 502.In particular, the command decoder 506 is used to generate internalcontrol signals to read data from and write data to the memory array502.

In some embodiments, the memory 500 may also include a voltage generator518 configured to receive a negative input voltage VNEG and to providean internal voltage VINTERNAL. The voltage generator 518 may be coupledto a protection circuit 514, such as an SCR. The protection circuit 514may help protect circuitry of the memory 500 in the event a relativelyhigh VNEG voltage is provided to the voltage generator, such as from anover-limit electrical event. Additionally, as previously discussed, theprotection circuit 514 may allow for modulating the trigger conditionsfor the SCRs included in the protection circuit 514. In someembodiments, the protection circuit 514 can be used in power-upsequences for the memory 500, as previously discussed. That is, while nopower is applied to the memory 500, the trigger conditions for theprotection circuit 514 are relatively low. In contrast, during power up,or after power has been applied to the memory 500, the triggerconditions for the protection circuits 514 are modulated to a highertrigger condition relative to when no power is applied.

From the foregoing it will be appreciated that, although specificembodiments of the disclosure have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the disclosure. For example, the protectioncircuit 514 may include the protection circuit 115 of FIG. 1, theprotection circuit 215 of FIG. 2, the protection circuit 315 of FIG. 3,the conductive path circuit 320 and the trigger circuit 330 of FIG. 4,or any combination thereof. However, the protection circuit 514 is notlimited to having the same design, and may be of different designs andinclude different circuitry from one another. For example, in someembodiments the protection circuit 315 of FIG. 3 may be configured toprotect against a negative over-limit electrical event, while anotherprotection circuit include circuitry configured to protect against apositive over-limit electrical event. Accordingly, the disclosure is notlimited except as by the appended claims.

Various illustrative components, blocks, configurations, modules,circuits, and steps have been described above generally in terms oftheir functionality. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present disclosure.

The previous description of the disclosed embodiments is provided toenable a person skilled in the art to make or use the disclosedembodiments. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the principles defined hereinmay be applied to other embodiments without departing from the scope ofthe disclosure. Thus, the present disclosure is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope possible consistent with the principles and novel features aspreviously described.

What is claimed is:
 1. An apparatus, comprising: a conductive pathcircuit configured to discharge current associated with an over-voltageevent at an input node responsive to a voltage of the input node havinga magnitude that exceeds a trigger voltage; and a trigger circuitcoupled to the conductive path circuit, the trigger circuit comprising:a first transistor coupled to the conductive path circuit and configuredto adjust the magnitude of the trigger voltage; and a lateral bipolarjunction transistor merged with the first transistor and wherein thefirst transistor and the bipolar junction transistor share at least twodoped regions.
 2. The apparatus of claim 1, wherein the conductive pathcircuit shares at least two doped regions with the trigger circuit. 3.The apparatus of claim 2, wherein the conductive path circuit comprisesa negative direction silicon controlled rectifier configured to limitvoltage between a reference node and the input node responsive to amagnitude of voltage differential between the input node and thereference node being more negative than the trigger voltage.
 4. Theapparatus of claim 3, wherein the negative direction silicon controlledrectifier shares a drain of the first transistor.
 5. The apparatus ofclaim 4, where in the silicon controlled rectifier comprises a firstbi-polar junction transistor coupled to a second bi-polar junctiontransistor, wherein the first bi-polar junction transistor is coupled tothe input node and the second bi-polar junction transistor is coupled toa reference node.
 6. The apparatus of claim 1, wherein the firsttransistor comprises a p-type field-effect transistor including a drainregion that is shared with the conductive path circuit.
 7. The apparatusof claim 6, wherein the lateral bipolar junction transistor includes anemitter region that is shared with the drain of the p-type field-effecttransistor.
 8. The apparatus of claim 1, wherein the first transistorcomprises a p-type field-effect transistor including a gate configuredto receive a voltage to which the first transistor is responsive toadjust the magnitude of the trigger voltage.
 9. The apparatus of claim1, wherein the lateral bipolar junction transistor includes an emitterregion that is shared with the conductive circuit.
 10. An apparatus,comprising: a protected circuit coupled to an input node; a protectioncircuit coupled to the input node in parallel with the protectedcircuit, the protection circuit including a conductive path circuit anda trigger circuit, the conductive path circuit coupled to the input nodeand a reference node and configured to provide a negative discharge pathbetween the input node and the reference node responsive to anover-voltage event at the input node, wherein the trigger circuit iscoupled to the conductive path circuit and is configured to adjust thetrigger voltage responsive to a voltage of a control node of the triggercircuit.
 11. The apparatus of claim 10, wherein the trigger circuit iscoupled to a control node, wherein the trigger voltage is adjusted bythe trigger circuit based on a voltage of the control node.
 12. Theapparatus of claim 10, wherein the trigger circuit is configured toadjust the magnitude of the trigger voltage to a first voltage while ina first state and to a second voltage while in a second state.
 13. Theapparatus of claim 12, wherein the first voltage is more negative thanthe second voltage.
 14. The apparatus of claim 10, wherein the triggercircuit includes a trigger transistor and a trigger bipolar junctiontransistor, and a body of the trigger transistor shares an n-well withat least a portion of the trigger bipolar junction transistor.
 15. Anapparatus, comprising: a protected circuit coupled to an input node; aprotection circuit coupled to the input node in parallel with theprotected circuit, the protection circuit including a conductive pathcircuit and a trigger circuit, the conductive path circuit configured todischarge a current associated with an over-voltage event at the inputnode responsive to a trigger voltage, wherein the trigger circuit isconfigured to adjust the magnitude of the trigger voltage, and thetrigger circuit includes a trigger bipolar junction transistor mergedwith a trigger field-effect transistor.
 16. The apparatus of claim 15,wherein the conductive path circuit shares with the trigger circuit afirst well doped with a first dopant type, and a second well doped witha second dopant type.
 17. The apparatus of claim 16, wherein the firstdopant type is an n-type dopant and the second dopant type is a p-typedopant.
 18. The apparatus of claim 15, wherein the conductive pathcircuit comprises a silicon controlled rectifier.
 19. The apparatus ofclaim 15, wherein the trigger bipolar junction transistor comprises aPNP bipolar junction transistor and the trigger field-effect transistorcomprises a p-type field-effect transistor.
 20. The apparatus of claim15, wherein the conductive path circuit is configured to discharge thecurrent associated with the over-voltage event at the input noderesponsive to a magnitude of a voltage difference between the input nodeand a reference node exceeding the trigger voltage.